Acute and Subacute Effects of Injury on the Canine Alveolar Septum: Results (3)

Transmission Electron Microscopy
In all six specimens examined by transmission electron microscopy (control as well as treated), gaps in the interstitium of the alveolar septum of lung alveoli were located predominantly at sites of junctions of alveolar septa and were occupied by type 2 cells (Fig 2 and 3; Table 2). This was especially prominent in the two- and four-week animals. In three of six animals (one untreated control and the 4-h and two-week papain animals), type 1 nuclei were predominantly distributed at junctional sites, while in the remaining three animals they were more evenly distributed along walls and at septal junctions (Table 3). Alveolar macrophages were predominantly located at septal junctions (72 to 100 percent) and in alveolar pores of Kohn (90 percent) in all animals in which they could be identified (Table 3). In one animal (4-h papain) most of the alveolar macrophages had disintegrated, along with the alveolar surface lining.
The prevalence of interalveolar pores of Kohn in the two- and four-week specimens was significantly lower as compared with controls. This was accompanied by thickened alveolar septa, especially in the four-week specimen, in which some septa showed two or three layers of capillary networks, suggesting alveolar collapse.

Figure_2

Figure 2. Transmission electron photomicrographs of type 2 cell from control animal. Type 2 cell is at an alveolar septal junction (where the septa of three alveoli meet), and in a septal interstitial gap. Therefore, it presents cell surfaces to two alveolar lumens, A, and A2. A3 marks the lumen of the third alveolar airspace. Note the normal appearance of this cell, including lamellar bodies (curved arrows). Capillary lumens marked by C (original magnification x 5860).

Figure_3

Figure 3. Electron photomicrograph of a type 2 cell at an alveolar septal junction from the specimen from the animal sacrificed two weeks after papain instillation. This type 2 cell occupies gaps in the interstitium of all three of the alveolar septa which meet at this junction. Compare markedly dilated cisternae of the rough endoplasmic reticulum (straight arrows) with Figure 2. The lamellar bodies (curved arrows), alveoli (A,, A2, and A5) and capillary lumens (C) are also identified. Portions of several other type 2 cells are also seen in this photomicrograph (original magnification x 5860).

Table 2—Pores and Other Septal Gaps

Untreated Control A Untreated Control B SalineControl Papain
4 h 2 Weeks 4 Weeks
Depth in jim* 47 48 35 83 31 46
Calculated surface area in iim*t 63,392 76,976 28,800 83,808 31,128 49,276
No. per No. per No. per No. per No. per No. per
1,000 jim 1,000 pin2 1,000 jtm* 1,000 jtm 1,000 jim2 1,000 jtm
SAt SAt SAt SAt SAt SAt
Pores
Total No. 2.3 2.8 2.9 2.9 1.7 0.6
Associated with cells 0.3 0.7 2.4K 0.3 1.5 0.4
Located at alveolar wall junctions 1.0 1.5 1.9 1.3 1.4 0.4
Septal gaps
Total No. 0.4 0.7 1.0 0.5 3.7 1.0
Associated with cells 0.3 0.4 0.5 0.4 3.2 0.9
Located at alveolar wall junctions 0.2 0.4 0.5 0.3 2.9 0.9

Table 3—Alveolar Epithelial Cells and Alveolar Macrophages

Untreated Control A Untreated Control B SalineControl Papain
4 h 2 Weeks 4 Weeks
No. per No. per No. per No. per No. per No. per
1,000 jjun2 1,000 p.m2 1,000 pm2 1,000 jxm2 1,000 p.m2 1,000 jim2
Alveolar Alveolar Alveolar Alveolar Alveolar Alveolar
Surface Area Surface Area Surface Area Surface Area Surface Area Surface Area
Type 1 cell nuclei: 0.5 0.5 0.9 0.4 0.9 0.5
Associated with pores/gaps 0.2 0.4 0.5 0.1 0.6 0.002
Located at alveolar wall junctions 0.3 0.3 0.5 0.3 0.6 0.2
Type 2 cells 0.4 0.3 0.7 0.8 2.7 1.2
Associated with pores/gaps 0.3 0.3 0.4 0.4 2.4 0.8
Located at alveolar wall junctions 0.3 0.2 0.6 0.5 2.2 0.7
Alveolar macrophages 0.2 0.3 1.1 0.4 1.4 0.6
Associated with pores/gaps 0.1 0.2 0.6 l.O 0.5
Located at alveolar wall junctions 0.2 0.2 0.8 1.3 0.5
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